So your ex has left you! Maybe it was your fault, maybe it wasn't, but the first thing you are going to have to do if you want to learn how to get your ex-girlfriend back is to take a cold hard look at yourself.
Analyzing yourself and trying to determine what it was that lead to your girlfriend leaving you is a crucial step you need to take before trying to regain your girlfriend.
Guys can be a little insensitive to woman's needs at times, it's not that we are deliberately being mean we are just wired different and place less importance on some things women find very important.
Once you have determined what you think pushed your lady away you are now ready to try to win her back.
The next step in learning how to get your ex-girlfriend back is also very important, DO NOT, I repeat DO NOT whatever you do grovel and beg your girl back, don't call her up too much and beg her to come back to you, the only thing this will do is reassure her she made the right decision to leave you.
You need to act as if you are getting on with your life, if you do talk is OK to express regret, but let her know you understand her decision, mention the things you have identified that you feel drove her away and how you are working on them.
By not pushing the issue of reuniting, she will discover some new found respect for you, she did want to be with you before, the new and improved you will make her want to be back with you.